The Australian Coastal Sediment Compartment data package consists of seven separate spatial data sets (2 point and 5 polygon) produced as a result of a 2012 technical workshop in which a panel of coastal science experts compartmentalised the Australian coastal zone. The three broad-scale polygon data layers - Coastal Realms, Regions and Divisions - capture high-level environmental attributes and information, and were developed as an informal hierarchy. These three data sets are supplied as they provide context and a logical sequence for the development of the compartments. With regards to spatial scale, a hierarchical listing for data sets is given below:
- Coastal Realms (1:5 000 000)
- Coastal Regions (1:1 000 000)
- Coastal Divisions (1:250 000)
- Primary Compartments and Points (1:250 000 - 1:100 000)
- Secondary Compartments and Points (1:100 000 - 1:25 000)
The Primary and Secondary Coastal Sediment Compartment (and Point) data sets represent a regional (1:250 000 - 1:100 000) and sub-regional (1:100 000 - 1:25 000) scale compartmentalisation of the Australian coastal zone into spatial units within (and between) which sediment movement processes are considered to be significant at scales relevant to coastal management. The Primary and Secondary Point data sets were generated and attributed using expert panel knowledge of coastal geomorphology and processes, and represent compartment boundaries along the coast at the respective scales. Environmental attributes used to determine the location of compartment (point) boundaries are given in priority order below.
1 - Gross lithological/geological changes (e.g. transition from sedimentary to igneous rocks).
2 - Geomorphic (topographic) features characterising a compartment boundary (often bedrock-controlled) (e.g. peninsulas, headlands, cliffs).
3 - Dominant landform types (e.g. large cuspate foreland, tombolos and extensive sandy beaches versus headland-bound pocket beaches).
4 - Changes in the orientation (aspect) of the shoreline.
Once generated, the compartment boundary point data were used in conjunction with a number of other input data sets to generate the Primary and Secondary Compartments.
The Realm, Region and Division data sets are interim products used to establish a context for the development of the Primary and Secondary points and compartments. There is no formal topological relationship between the Realm, Region and Division data sets. An informal hierarchical (not topological) relationship does exist between the Primary compartments and the Divisions, as seen in the Primary compartment attribute field `ID_Primary. The Primary and Secondary compartments do share a formal topological relationship, and also a formal hierarchical relationships, as shown in the Secondary compartment attribute field `ID_Secondary.
Primary compartments are intended to be representative at a spatial scale of 1:250 000 - 1:100 000 while secondary compartments are intended to be representative at scales from 1:100 000 - 1:25 000.
IT IS IMPORTANT TO NOTE THAT THE COMPARTMENT POLYGON DATA IS NOT ATTRIBUTED WITH ENVIRONMENTAL DATA - ONLY THE PRIMARY AND SECONDARY POINT DATA SETS CONTAIN SUCH ATTRIBUTE DATA.
Maintenance and Update Frequency: asNeeded
Statement: The user is referred in the first instance to Geoscience Australia Record 2015/025 (The Australian Coastal Sediment Compartments Project: Methodology and Product Development) for further information.
The method used to create the polygon extents for the Realms, Regions and Divisions is not recorded but a review of the products suggests that they have not been derived from a digital elevation model or from buffering the coastline. It is believed the extents were digitised on-screen by hand with no further review of the extents, e.g. not clipped back to within Australia's Exclusive Economic Zone (EEZ). In developing the Primary and Secondary Compartment (polygon) data sets, the input data sets and basic process are presented below.
Input data sets
- The Australian Bathymetry and Topography Grid 2009 (used to define onshore and offshore bathymetric/elevation limits)
- Primary and Secondary boundary points defining compartment limits on (or near) the coastline
- Break lines connecting the landward to seaward extent via the Primary and Secondary compartment boundary points
o Manually digitised on-screen through visual interpretation of the Australian Bathymetry and Topography Grid and SPOT/Landsat optical imagery to define onshore topographic barriers to sediment movement (e.g. ridges.
- Australia's Exclusive Economic Zone (EEZ)
Process steps, completed within ESRI ArcGIS 10.2 suite, to create the Primary and Secondary compartments included:
- Create the bathymetric/elevation contours (+50 m, +25 m, -50 m and -130 m) from the Australian Bathymetry and Topography Grid
- Select smaller features via attribute query and visually verify features are not significant before deleting
- Convert the contour lines to polygons
- Clip the polygons with the EEZ polygon to ensure the compartment envelopes do not exceed Australia's EEZ
- Extract (using the 'Erase' tool) the polygon between the inland and offshore limits for each of the Primary (+50 m to -130 m) and the Secondary (+25 m to -50 m) polygons
- Create the compartments by applying the `Split Polygons tool within an edit session with inputs of the compartment envelopes and the break lines
- Manually attribute compartments with a sequential number starting at the tip of Cape York and travelling in a clockwise direction.
- Via a Python script, attribute the Primary and Secondary polygons with a unique identification number composed of State (alpha), parent compartment (numeric) and a sequential number representing the order of occurrence of the primary compartment within the parent compartment e.g. QLD0101, QLD0102. The parent compartments are Coastal Divisions for the Primary compartments and Primary Compartments for the Secondary Compartments